Is this Control Magic homebrew spell balanced? (Spell-stealing counterspell)

Question

I based this off of Counterspell, with higher level requirement as it seems to me that it is generally a more useful spell.

Control Magic

Fifth level abjuration

Casting Time: 1 reaction, when you see a creature within 60 feet casting a spell
Range: 60 ft
Components: V, S
Duration: Instantaneous

You attempt to take control of a spell a creature is casting. If the creature is casting a spell of 5th level or lower, its spell fails and has no effect. If it is casting a spell of 6th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, you may change the target of the spell to any other valid target for that spell within range. If the spell requires concentration, you also become responsible for concentrating on the spell.

Is it balanced like this? Are there spells which would interact with it in unexpected ways?

Answer 1

This spell is too strong

Rules as written you do not know what spell the opponent is casting when they are casting it. Based on an optional rule in Xanathar's Guide to Everything, you can use your reaction to make an Intelligence (Arcana) check to find out, but then you cannot use it for Control Magic anymore, leaving you with the choice to try and learn what is cast, or counterspelling/controlling it blindly.

As you do not know what spell is cast, you also do not know what legal targets you can pick, and have to pick blindly. If you pick an illegal one, then the spell is just wasted, which may be fine, as it works as a counterspell of sorts. If you pick a legal one, the spell can become extremely powerful, not only negating the opponents action, but giving you a free one, and possibly a free higher level spell slot on top.

The problem is that even in this setup where you do not know what they are casting, the spell is better than counterspell in many ways.

A typical combat encounter is just 3 rounds, or maybe 4-5. That means that most opponent spell casters lead with their high-level, high impact spells to maximize their effect and ability to impede the party: they do not know if the party has this spell, or counterspell, and trying to trick the party into wasting counterspells by betting on that and leading with low-impact cantrips is an ineffective and unlikely strategy when the party fighters and sharpshooters are busy slicing you up. So we can expect to capture high level spells with this, by the time we can cast it.

If you always pick a spot near the opponent as the target, the effect will be that if the spell is a beneficial or harmful one targeting a creature, it will be lost, just as with counterspell. If it is an area effect with a target location, there is a chance that it is some beneficial effect the opponent cast on their area which would waste the Control Magic, but the majority of such spells in combat are harmful area effects that target the party.

I think because of this, the spell is not well balanced. The baseline to compare against is counterspell, which is a real contender for the best spell in the game. I think any spell that is potentially stronger than counterspell should be looked at very critically. This essentially is counterspell for spells up to level 5, just as if you upcast counterspell to level five. For higher level spells, it either is counterspell, or, more likely than not, counterspell that gives you a free level 6+ spell to harm the opponent with on top. I do not think the off chance of the spell being a beneficial area effect and still working is making up for it.

Answer 2

It depends on how you rule on knowledge of spells cast at your table.

There are three different ways that I have played counterspell, and its usefulness depends significantly on which of these ways you use:

1. The DM says "The bad guy casts fireball." The player says "I cast counterspell."
2. The DM says "You see the bad guy casting a spell." The player says "Can I tell what spell?" Some sort of ability check or contest happens, and then the player gets to decide to cast counterspell after it all resolves.
3. The DM says "You see the bad guy doing what looks like spell casting." The player decides to cast counterspell or not.

These three rulings differ in the level of access the player has to what spells the NPCs are casting. Greater access to this knowledge makes counterspell more powerful. In (1.), knowledge is complete, and your counterspell is never wasted. In (2.), sometimes you have complete knowledge, and sometimes you are forced to choose between saving your slot and gambling on incomplete knowledge. And of course, (3.) is a total crap shoot, you don't even know if the target is actually casting a spell or just waving their hands around.

Now, on to your spell. If (1.) is how your table handles spellcasting and counterspell, I think this makes your spell too good. You always know when it would let you steal the target's high level spell. This makes it essentially equivalent to trading a 5th level spell slot for a 6th level or higher spell and cancelling the casting by your enemy. This is a horribly unbalanced effect, way stronger than 5th level.

If your table uses (3.), then the spell is fine, at least, in terms of tradeoffs. Its huge potential is offset by the possibility of wasting it on a target that was casting a cantrip. However, it might feel kinda crappy to waste on a cantrip, and has potential to cause conflict in the spirit of "you changed it to a cantrip because I was going to steal it". While on paper it may be balanced under (3.), I think it has practical issues that make it not so great of a fit.

Finally, (2.) is the middle ground where I think the spell could work. Sometimes you can count on it for a huge tide-turning effect, and sometimes you have to take a gamble. That's the closest thing to balance we can get on paper with this spell, I think, and I would be comfortable deploying this spell for playtesting in the context of (2.) only. Definitely not for (1.) or (3.).

Answer 3

This spell is potentially too strong, as it allows you to 'cast another spell' using your Reaction.

Even if you can't control what spell that is, that will be an issue for a lot of tables. Not all, as a 5th level spell slot can be weaponized rather heavily in the right hands, but for many.

Technically Counterspell already does this - by negating an enemy spell, you're '1 spell up', but this allows you to get '2 spells up' potentially, and anything active (damage done, conditions applied, healing done etc) is always considered 'stronger' than anything that negates enemy action (counterspell, grappling, stunning).

Fix this by having Control Magic use up your next Action.

This 'balances the scales' and will make it far more palatable to those worried by overpowered things. Allow the caster to understand what spell they have controlled, and on their next turn, have the option to redirect it as they choose as their Action. This allows it to either be a 5th-level-slot Counterspell, or, something which steals a spell for your own use - up to the individual caster as to whether they want to spend their Action doing so. This makes the spell still potentially quite useful, but more limited in scope. Still potentially a waste if you Control Magic a cantrip, but with the potential to give you a spell you don't have access to, save you a powerful spell slot while negating the enemy's spell, and or even grant you a spell of a level you don't currently have access to (if fighting a higher-leveled caster).

I'd also change it to allow the redirection of lower than 5th level spells, as if someone wants to as a 9th level+ caster use their Action redirecting their opponent's 3rd level Magic Missiles or w/e, then that's fine by me. And for someone using this spell a lot, that's the kind of thing they'd get a kick out of.